1. Field of the Invention
This invention relates to an elecrically heatable automobile glass pane with printed-on and baked-in, thin heating conductors disposed on one surface, which conductors are connected with collecting conductors, disposed along the edge of the glass pane and printed-on and baked-in simultaneously with the heating conductors, metal strips being disposed on the printed-on and baked-in collecting conductors and being electrically conductingly connected with them.
2. Description of the Related Art
Electrically heatable automobile glass panes are used especially as rear window panes in automobiles. If the collecting conductors, which serve for electrical supply to the heating conductors, consist only of the printed-on and baked-in conducting material of which the heating conductors consist, they must be made relatively wide in order that their electrical resistance shall not become too high, since otherwise they become too hot. However, even if made relatively wide, their electrical resistance is still high on account of the extraoridinarily small thickness of the printed-on and baked-in coating. Even with a relatively wide construction, it is usually not possible to avoid a portion of the electrical energy becoming lost due to the undesired heating-up of the collecting conductors.
For avoiding this disadvantage, it is known to reduce the electrical resistance of the printed-on and baked-in collecting conductors by the provision of a metallic conductor, for example a strip of copper sheet or a flat strand of copper (U.S. Pat. No. 3,467,818). The metal strip is here soldered, for example at intervals, to the baked-in collecting conductor. In order to prevent harmful mechanical stresses from occuring due to the different coefficients of thermal expansion of the metal strip and of the glass pane, which could lead to fracture of the soldering points, the metal strip is convex curved in the manner of a bridge span in the regions between the solder points. The printed-on and baked-in collecting conductors can be of relatively thin construction in this known heated pane.
Heated panes with such reinforcing strips soldered onto the collecting conductors in turn have other disadvantages. Firstly, the metal strips projecting on the surface represent a nuisance in packaging and handling the glass panes, and it can easily happen that if the soldered-on metal strps are bumped or knocked, they bend or the solder points become loosened. Furthermore, such collecting conductors reinforced by metal strips are especially disadvantageous when the collecting conductors are disposed not at the outermost edge of the glass pane, but at a distance from the pane edge and within the viewing field, which is inevitably the case when the heating conductors are used also as radio antenna conductors. In this case, the collecting conductors must be disposed at a distance of a few centimeters from the frame of the bodywork, because otherwise the capacitance of the antenna conductors adopts unacceptably high values. In such a conductor network, serving both as antenna and as heating resistor, there are advantages in constructing the collecting conductors, which are situated entirely in the viewing field, to be as narrow as possible, which can best be achieved by reinforcing them with an additional metal strip. On the other hand, the provision of an additional metal strip is a nuisance, because the metal strip is not only an obstruction, for example when cleaning the glass pane, but because in particular there is a risk that the additional metal strip, when the glass pane is cleaned or in other circumstances, may be so heavily stressed that the connection points with the baked-on coating of the collecting conductor become loosened.